Structural Diversity and Tunable Emission in Hybrid Organic–Inorganic Copper(I) Bromides

Recently, hybrid organic-inorganic copper(I) metal halides have attracted global attention due to their intriguing optical properties and low-cost solution processability. In this work, we report three hybrid organic-inorganic copper(I) bromides, [TMPA]₂[Cu₂Br₄], [TMPA]₄[Cu₆Br₁₀], and [TMPA]₂[Cu₄Br₆], synthesized through a slow evaporation method using trimethylphenylammonium (TMPA⁺) as the organic cation. By precise control of the CuBr and TMPABr precursors, different copper halide [Cu₂Br₄]²⁻, [Cu₆Br₁₀]⁴⁻, and [Cu₄Br₆]²⁻ structural units can be obtained. [TMPA]₂[Cu₂Br₄], [TMPA]₄[Cu₆Br₁₀], and [TMPA]₂[Cu₄Br₆] demonstrate distinct blue, orange, and greenish-yellow light emission, respectively. The first two compounds have zero-dimensional (0D) crystal structures in centrosymmetric triclinic space group P-1 and monoclinic space group P2₁/n. In contrast, [TMPA]₂[Cu₄Br₆] features a unique one-dimensional (1D) structure and crystallizes in the centrosymmetric monoclinic space group P2₁/c. Consequently, the observed greenish-yellow emission of [TMPA]₂[Cu₄Br₆] is also unique, in contrast to the typical orange-red emission of 0D [Cu₄Br₆]-based compounds. This work provides insights into the design of copper halide light emitters and emphasizes the influence of structural dimensionality on photoluminescence. The tunable optical properties suggest the potential of these materials for multicolor photopatterning, information encryption, and anticounterfeiting applications.